Freedom of speech campaigners are claiming victory as the House of Lords is expected to back changes removing "anachronistic" laws which have criminalised libel for more than 700 years.

The changes, which will be debated as part of the controversial coroners and justice bill, repeal laws dating back to 1275 and allow "extremely serious" libel and sedition to be prosecuted in criminal courts. The laws have long been regarded as an impediment to freedom of speech and an anomaly in the UK, which has encouraged countries with repressive regimes not to conduct prosecutions for libel.

"The abolition of sedition is long overdue," said Geoffrey Robertson QC, who successfully defended Salman Rushdie in the last sedition case held in Britain, over Rushdie's book, The Satanic Verses. "This law is still used throughout the Commonwealth by repressive governments to jail their opponents. Its abolition here ensures that those governments can no longer use the excuse that they are merely following British law."

Agnes Callamard, executive director of campaign group Article 19, said: "This will send a very strong and clear signal globally that democracies do not have criminal defamation laws." The government's admission that the law, which has been widely recognised as hampering freedom of press and political dissent, must change comes after increasing concern about clampdowns in other countries, including many states in Europe and the Commonwealth.

"These common law offences are anachronistic and their continuing existence, albeit seldom used, has been cited by other countries as justification for the retention of similar laws, which have been actively used to restrict media freedom," a Ministry of Justice spokesperson said.

"The UK is committed to encouraging other countries to recognise and respect freedom of expression and the media must take the lead in abolishing these out-of-date offences."

But support for repeal comes as the government faces continuing pressure to extend changes to the law on blasphemous libel – which will also be debated – to Northern Ireland, where offensive remarks about the Christian church remain an offence.

The Guardian has learned that senior political figures from Northern Ireland will join calls in the Lords for the provisions to be extended, including Lord Alderdice, former speaker of the Northern Ireland assembly, and Lord Eames, the former archbishop of Armagh.

"There is now a grotesque situation in Ireland," said Liberal Democrat peer Lord Lester QC. "In the Republic of Ireland, there has been a rebirth of the offence of blasphemous libel for domestic constitution reasons, and in Northern Ireland we have not yet managed to get rid of it.

"God no more needs to be protected by criminal law in Northern Ireland than in Great Britain."

The government denied it was considering extending the repeal of blasphemous libel to Northern Ireland. "The government believes that the Northern Ireland assembly is the best forum to consider this area of law as it relates to Northern Ireland," the Ministry of Justice said.

Freedom of speech groups were also critical of proposals on "criminal memoirs" – expected to be debated later this week, which would confiscate profits from convicted criminals who sell books about their offending. The controversial measures were proposed in response to cases such as that of Mary Bell, who was convicted for killing two children and was later paid for her contribution to a book.

"The measures we are proposing in the coroners and justice bill will give courts the power to order offenders to pay back benefits they have obtained from exploiting information about their offences," a Ministry of Justice spokesperson said. "It is wrong for convicted criminals to profit from their crimes, whether directly from the proceeds of the crime itself or indirectly through cashing in on the story of their crime."

The government said courts would have a discretion in imposing the orders, but critics argued the sweeping scope of the powers may compromise "genuine rehabilitation" and encompass artwork and interviews as well as books.

"There are a few very harsh cases in which one sympathises greatly with the victims of serious crime, when a convicted criminal writes about terrible and evil conduct, but the government's reaction enables the state to confiscate the profits of a much wider range of criminal memoirs," said Lester.